Does Gas Evaporate in The Boat Tank?

Does Gas Evaporate in The Boat Tank?

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Does Gas Evaporate in The Boat Tank?

Gas is an explosive mixture of hydrocarbons, mainly methane and oxygen, that occurs in the presence of heat and the absence of air.

It’s primarily used as a fuel to power various processes in the industry, such as burning fossil fuels for energy production or heating homes and buildings.

Organisms also use it as a source of chemical energy, where it’s released from digested food during certain fermentation processes to generate (in addition to carbon dioxide) ethanol and heat.

Yes! Gas in a boat tank will evaporate at up to 5-20% on the first day. This is due to the Gas in the engine being very moist, and there is no sunlight penetration. When Gas evaporates, it releases heat and water vapor into the air.

The moisture and water vapor will then condense on surfaces inside your boat or even on anything wet within 10 meters of your engine, such as a person’s skin or clothing.

Gas can take up to 12 hours to evaporate in the tank when the boat is on a trailer, and the engine is running.

Contrary to popular belief, opening up the tank hatch and leaving it open for 24 to 48 hours will not stop Gas from evaporating.

If you want to stop Gas from evaporating in your tank, you can use an ignition system that does not depend on Gas for ignition. Such systems are electric, mechanical, or chemical.

The only way to avoid Gas escaping from your engine is to shut the engine off and disconnect it from the fuel tank at least 24 hours before heading offshore.

Alternatively, the best way is to remove the fuel tank and lock it up in a secure area if you leave your boat unattended for several days.

Why Should You Never Fill a Boat Gas Tank?

Filling your boat’s gas tank leaves no room for gas expansion. In the event of overfilling or improper storage, the Gas expands and creates a vacuum in the tank.

This decreases fuel efficiency and can lead to serious engine problems, including damage to gaskets, hoses, and valves.

It’s best to fill your tanks only 3/4 of the way full so that there is always room for gas expansion. When ready for a refill, top it off by pouring more Gasoline into your tank until you’re up to 3/4.

Also, be sure to keep your tank vented to allow fumes to escape. If fuel vapors confine in the tank, they could cause a dangerous gasoline vapor explosion.

To vent your fuel tank, open one of the drain cock holes at the bottom of your tank. A non-return valve inside prevents Gas from draining out if you forget to close the drain cock after refueling.

This valve also vents air from inside your tank when you fill it.

If your engine has a fuel gauge, the tank gets vented when the pointer is in the full position. If your engine has no gauge, it’s vented if you can see the light at any of the vent holes.

For How Many Miles on One Tank of Gas Can a Boat Travel?

It depends on your boat and the size of the tank that it uses. On a full tank of Gas, a 25-horsepower boat can travel about 500 miles, and a 40-horsepower boat can travel about 600 miles before needing to refuel.

Here is a table showing the average mileage.

Type of BoatMiles
Aluminum Fishing Boats5 to 10 miles
Bass Boats5 to 10 miles
Bay Boats5 to 30 miles
Bowrider Boats3 miles per gallon
Cabin Cruisers5 to 30 miles
Center Console Boats1 to 2 miles per gallon
Deck Boats5 to 30 miles

Where Do You Store Extra Fuel on A Boat?

Boat PartDescription
 On The Deck– You can store your extra fuel on the deck of your boat. If you ever anchor close to the shore, you can refill the tank at a nearby service station.

– In the event you are at sea and are running out of fuel, you can use your fuel dump to siphon the available Gas from your engine.

– You will need to ensure that there is no gas in the intake tube before using it. Use a rag to wipe all the icky residue off it, and then pour some fresh gasoline into the tube.

Your boat should run with less than a gallon of Gas in its tank.
In The Bilge– There is a space below the floor of your boat that is perfect for storing extra fuel. It’s a little dark down there, but if you have a flashlight, you’ll be able to see quickly enough.

– You need to ensure that the Gas is well above any water lines. It will leak and ruin some of your other items in the bilge if it gets wet.

– Anchor away from shore because this is where most people expect you to store your fuel. If they find it here, they’ll assume that you have already refueled and will leave you alone.
In The Tanks– The last and most dangerous place to store extra fuel is your gasoline tanks. Ensure that there are only water lines or hoses inside the tanks if there is enough room to hold a few gallons in the tanks.

This allows the Gas to get into them and leak. – If you will use this option, be very careful because the only thing you have protection against fire is a glass jar full of Gasoline.

Gasoline is a highly flammable liquid. It is explosive and extremely hot when it goes off. – The fuel tank could explode if you hit something with your boat. It could also explode if you get hit with a wave.

– If you decide to store fuel in the tanks, it must be in a glass jar. Do not leave the Gas in any other container because the fumes can ignite easily.

– You’ll need to use an extra line to siphon the Gasoline out of your tank and away from your boat, just in case it ignites.

It is never safe to have a fire on a boat this small, so make sure you can get away from any flames fast.
In The Spare Fuel Tank– The last option is to store the extra fuel in your spare tank. You will need to ensure a drain hole on the bottom of your boat and plenty of room inside it for all the Gasoline.

– This space, especially when empty, can be dangerous because any spark could cause an explosion. When doing this, ensure you are not near any other boat anchored up close.

How Do You Remove Fuel from A Gas Tank?

Start by pulling the fuel lever in the bow to release the fuel from both tanks. You can locate this on the left side of the boat’s steering console.

Next, grab a 5/8-inch wrench and remove both caps from each tank, one for each tank.

Grab your hose connected to a garden sprayer or small hand pump and begin pumping out as much Gas as possible until you reach near empty on one tank.

As you pump the Gas out of the tank, spin the fuel lever to help move the remaining Gas from the tank down to that pump.

Once you reach near empty on one tank, begin pumping out the remaining Gas from both tanks until empty. Be sure to switch back and forth between tanks when pumping.

Once you have turned off your engine, let it sit for 30 minutes to give all the fuel time to drip into your catch container.

Does Gas Evaporate in The Boat Tank?

Once you drip all fuel out of the tank, turn your engine back on and spin your fuel lever to pump the remaining Gas sitting at the top of your tank down to the pump.

After a few minutes, remove both caps from both tanks and replace them with new caps. You are now ready to fill up and get back on the water.

10 Steps for Removing Gas from A Boat Fuel Tank

1: Have a spare fuel tank (available at most marine supply stores) and a portable manually operated crank-operated vacuum pump with quick-release fittings.

2: If the boat has a floating gas tank with a manual drain valve, drain the fuel tank and remove these parts.

If not, connect the quick-release fittings to an empty house, add 5 gallons of water and drain the fuel tank from a 90-degree angle until it is empty.

3: Attach your vacuum pump to an air hose and begin pumping through it. The vacuum pump will pull all the air out of the system.

If there is no air in the system, the pump will begin to pull water from your bilge. You can then redirect it to the empty fuel tank and continue until no water is in sight.

4: Place ten pounds of absorbent material (available at a marine supply store as “Boat Drain”) in your drained fuel tank. This will absorb any gas fumes that are present. You can now fill the tank with clean fuel.

5: Fill your boat’s gas tank with clean fuel.

6: Set the float valve on your fuel tank so it will not overflow.

7: Replace your manual drain valve with a standard valve.

8: Purchase a fuel tank vent and cap to divert air from the fuel tank. This is usually only necessary if your boat has no gas or a faulty gauge.

9: Use one of the following methods to remove any remaining gas fumes.

  1. To flush the system, you can use a pressure washer, running the hose under pressure while removing all residual fuel.
  2. Many boats, including many sailboats, have a hose that connects to the vent on one side of the boat and then connects to an air vent in an outboard motor on the other side.
  3. Blow with compressed air through this hose into this vent until no more fumes are present.
  4. Run a vacuum pump (available at marine supply stores) for an hour or two to remove any remaining gas from the bilge.
  5. If none of these methods work, you may need to clean your fuel tank professionally.

10: Once your tank is clean, you can use the float valve to keep it from overflowing and replace it with a standard valve that will allow you to monitor your fuel level at a glance.

Is The Fuel Tank Equipped with A Drain Plug?

Some boat fuel tanks have a drain valve that allows you to periodically empty water and sediment from the tank. This reduces corrosion of the tank and helps prevent accidents.

It also prevents a buildup of sediment that can cause flooding in your engine compartment.

If you’re concerned about your Gasoline or diesel fuel supply, check that you install a drain valve in your fuel tank. If not, part of the expense involved in replacing your boat’s fuel tank might be unnecessary.

Most manufacturers recommended drain system that allows draining up to at least half an inch (1.3 cm) of water per hour.

It includes a long-life rubber seal to minimize leakage, and you can service it by removing two screws from the fuel tank’s bottom shell.

It is best if you never submerge the tank or use it in any manner that might cause damage to its rubber gasket.

Marine diesel fuel systems typically have drain pumps that you can service easily by removing a few screws.

They may or may not have a high-pressure fill hose, a separate assembly you will typically have to replace if it leaks.

Determine whether the fuel tank has such a serviceable drain valve and replace it if necessary.

How To Seal a Gas Tank Drain Plug

First, find the gas tank drain plug or the outlet for emptying the fuel tank. This will be a hole on the side of your boat with a plug in it.

Wait until you’re ready to refuel (or if you want to find out how much Gas remains), then remove this plug and empty any remaining gasoline into an approved container.

Next, take an appropriately sized bolt and thread it through one of the holes/eyes on your rubber washer. Do this to both your gas tank drain plug and your gas tank outlet.

After passing the bolt through both holes, wrap your rubber washer around the bolt. Tighten the bolt by hand until the rubber washer squeezes tightly on the bolt, but not enough to turn it.

Next, take another rubber washer and place it under one of your bolts from above. Place your bolt through your rubber washer from below and tighten it by hand.

Finally, use a pair of pliers to squeeze the rubber washer tightly around the bolt and test for leaks. If you have leaks, continue using your original rubber washer as a spacer between the bolts.

Remember, if you need help determining what size washers to use, try 1/2 inch or 5/8 inch. If you have a larger diameter bolt, use a larger size washer. You can find rubber washers at most auto parts stores or online.

For How Long Can You Leave Gas in A Boat?

You should use Gas within a month of purchase to ensure that it is not old, degraded, or contaminated.

Exposing Gasoline to changes in temperature and humidity will deteriorate in quality more quickly. If you are still determining the age of your fuel, the best idea is not to use it and replace it with fresh fuel.

The best advice for fuel transportation is to have a good container for refueling. For example, gas cans and plastic buckets are better than bags or bottles, which can damage during transport and storage.

For motorboats with no electric engine, it is suitable that the gas tank has a capacity greater than two hours of cruising per tank.

I recommend always refueling your gas tank with fresh fuel, especially when traveling long distances.

Before you leave, you should thoroughly clean your tank. This process will remove the sediment accumulated in your fuel tank over time.

Add a fuel stabilizer. I recommend adding STA-BIL Fuel Stabilizer to reduce the amount of fuel degradation during storage and travel.

This product will also inhibit bacteria or algae growth in the fuel tank, which can deteriorate gas quality while traveling between ports or storage.

How Much Gas Over the Winter Should I Put in My Boat?

On average, a boat holds up to 15 gallons of Gas if it has a 40-gallon tank.

It’s vital to know how much you should put in your boat, however, because adding too little fuel can cause the engine to run too lean, and the boat will not operate properly;

Adding much fuel causes the engine to run rich and exhaust fumes into your living space. Don’t overfill your tank; you could risk polluting water and killing marine life.

Most boat owners follow this rule: Fill your tank to the bottom of the filler cap and then add a half-gallon or so of water to ensure no air pocket in the tank.

If all goes well, you should be good for winter. But for some people, winter can be very cold in colder states like Alaska.

Being warm is nice, but you should also have enough Gas in your tanks to stay supplied with Gas. Here is a simple breakdown.

Type of BoatGas
Aluminum Fishing Boats1 to 4 gallons per mile
Bass Boats1 to 4 gallons per mile
Bay Boats1 to 4 gallons per mile
Bowrider Boats1 to 4 gallons per mile
Cabin Cruisers1 to 4 gallons per mile
Center Console Boats1 to 4 gallons per mile
Deck Boats1 to 4 gallons per mile
Dinghies1 to 4 gallons per mile

Does Shower Water Go to The Holding Tank On A Boat?

Yes! The sinks, showers, and toilets on your boat drain into a common waste holding tank. You can locate the holding tank on deck at about mid-ship.

This tank collects all the wastewater from the boat and pumps it overboard before returning to the ocean’s surface. No, it does not return to your shower water but to the ocean’s surface.

This is okay because septic tanks have a rate for holding up to 500 gallons of sewage and toilet waste and will work well in this environment.

A common concern is how to empty and clean out this holding tank. The holding tank gets cleared out of “salt water,” not salt, but the concentrated salt that we get in the ocean from ocean winds.

Salt water might mix with the holding-tank contents and become lodged in drains and fittings, but this is not due to salt buildup.

Please realize that this waste holding tank will have a large volume of water on board and a strong ocean breeze.

In these conditions, this system, designed to keep everything outside, stays clean all the time.

If you go out in the sun, it is a good practice only to go directly bang into the fresh-water shower facilities if there are no guests on board.

There are plenty of systems capable of doing this, and you can use any of them. You will have to talk with some marine maintenance shops, which should choose the best one for your boat or yacht.


Boat gas tanks can be a little tricky to understand. Because you spend most of your time at sea, it is important to stock yourself fully with fuel.

Storing the extra fuel on your boat could be better because of the fumes, but if you think of a creative method, it can work out well for you.


Hi! I' am Tom. I was a manager in one of the biggest stores for over 10 Years, am also an SEO by night. I don't like to call myself a blogger; they are very analytical, do email marketing, and know all SEO stuff. I faced many questions from customers about different products, and there was hardly any help on the internet. After learning all the things about these products as a manager the hard way, I decided to start a blog and help other people.

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